Pressure indicator and bypass pressure relief valve

ABSTRACT

An indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, which indicates or signals an increase of pressure in the high-pressure side of the system beyond a predetermined differential limit; and bypasses fluid from the high-pressure side to the low-pressure side of the system to relieve such high pressure whenever it exceeds a predetermined differential pressure limit.

United States Patent lnventor Kurt F. Hammer Carnarillo, Calif.

Appl. No. 876,374

Filed Nov. 13, 1969 Patented Dec. 7, 1971 Assignee Purolator, Inc.

Rahway, N.Y.

PRESSURE INDICATOR AND BYPASS PRESSURE RELIEF VALVE [56] ReferencesCited UNITED STATES PATENTS 2,998,138 8/1961 Mould et al 210/903,128,743 4/1964 210/90 X 3,150,633 9/1964 210/90 X 3,364,897 1/1968210/90 X 3,371,787 3/1968 210/90 3,420,266 1/1969 137/553 PrimaryExaminer-Henry T. Klinksiek Attorney-Wham & McManigai ABSTRACT: Anindicator and bypass pressure relief device for use in a system having ahigh-pressure side and a low-pressure side. which indicates or signalsan increase of pressure in the high-pressure side of the system beyond apredetermined differential limit; and bypasses fluid from thehigh-pressure side to the low-pressure side of the system to relievesuch high pressure whenever it exceeds a predetermined differentialpressure limit.

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r e 4 a5 5 5-36 e75 52 r 64 A "44 PRESSURE INDICATOR. AND BYPASSPRESSURE RELIEF VALVE BACKGROUND OF THE INVENTION My invention is usefulin different arts but has a special utility in fluid or hydraulicsystems or lubrication circulating systems such as employ a filter forfiltering the fluid. When a filter starts to clog there is a gradualincrease in back pressure on the high-pressure side of the system; andwhen this back pressure produces a predetermined differential inpressure between the high-pressure side and the low-pressure side of thesystem the filter must be replaced.

Also, an increase of pressure in the high-pressure side of such a systemmay occur due to pressure surges of different durations which would alsocause the differential pressure between the high and low sides toincrease above a predetermined limit.

Prior to my invention there were devices on the market for indicatingsuch increases in differential pressure and such surges in highpressure, one such device being disclosed in the US. Pat. to Mouwen, No.3,364,897, granted Jan. 23, I968.

Clogging of the filter or' high-pressure surges may cause such anincrease in pressure on the high-pressure side of the system that damagemay result. Present prior art devices known to applicant do not solvethis problem and there is,

therefore, a need in these arts for a device which will visually oraudibly indicate an increase in differential pressure whenever itexceeds a predetermined limit and which also will automatically bypassand relievethe pressure in the high-pressure side whenever suchhigh-pressure exceeds a predetermined limit which might cause damage.

SUMMARY OF INVENTION My invention provides a device which is connectedon one side to the high-pressure side of such a system, and on the otherside to the low-pressure side of such system, and which functions togive an indication whenever the pressure differential between thehigh-pressure side and the low-pressure side exceeds a predeterminedlimit, and which further functions to bypass fluid from thehigh-pressure side to the lowpressure side in order to relieve highpressure whenever the differential in pressure exceeds a secondpredetermined limit. It is an object of my invention to provide apressure indicator and bypass pressure relief device in which a movablepressure responsivemeans subjected to high pressure on one side and lowpressure on the other side, functions to control the operation ofdifferential pressure indicator means and also to control a bypasspressure relief means depending upon the magnitude of the pressuredifferential. I

It is another object of my invention to provide a device of thecharacter described in which the pressure-responsive means is in theform of a piston which moves in response to differential pressures andwhich causes the operation of the indicator means and the bypasspressure relief means.

It is a still further object of my invention to provide a device of thecharacter referred to in which there is an indicatoroperating means foroperating the indicating means, which indicator-operating means iscarried by the pressure responsive means but is not exposed to the highpressure side of the system in which the device is incorporated, and inwhich the indicator-operating means is movable relative to thepressureresponsive means. It is also an object of my invention toprovide a pressure indicator and bypass relief device in which theindicator-operating means is carried by the pressure-responsive meansand is directly exposed to the high pressure on the high-pressure sideof the pressure-responsive means.

It is another object of my invention to provide a device of thischaracter in which small valve leakages from the highpressure side tothe low-pressure side of the system will not cause malfunctioning. It isa further object of my invention to provide a device of the characterdescribed in which an increase in pressure on the high-pressure sidemoves the pressure-responsive means into an indicator actuating positionand in which a further increase in high-pressure moves thepressure-responsive means into bypass pressure relief position.

It is a still further object of my invention to provide a device of thecharacter referred to in which the indicator means and the indicatoroperating means each have associated magnets with similar poles onadjacent sides whereby the movement of the indicator-actuating meansinto a position near said indicator means will cause movement of saidindicator means into an indicating position as the result of therepelling action of the magnets.

Another object of the invention 'is to provide a fluid or hydraulicsystem having a low-pressure side and a high-pressure side with themeans connected between the high-pressure side and the low-pressure sidefor indicating increases in differential pressures and for causingbypassing of fluid from the BRIEF DESCRIPTION OF THE DRAWINGS Referringto the drawings, FIG. 1 is a diagrammatic view illustrating a portion ofa system incorporating the features of my invention;

FIG. 2 is a longitudinal sectional view through a pressure indicator andbypass v pressure relief device incorporating the features of myinvention, this figure illustrating the position of the parts in anormal nonindicating and nonbypassing position;

FIG. 3 is a view similar to FIG. Zbut showing the position of the .partswhen the pressure in the-.highpressure side of the system has risen to apressure difl'erential limit where an indication of such conditionshould be made;

FIG. 4 is a view similar to FIG. 2 but showing the position of the partsin bypass pressure relief position;

FIG. 5 is a cross-sectional view taken on the line 5-5 of FIG. 2;

FIG. 6 is a longitudinal sectional view through a second deviceincorporating the features ofmy invention, the parts in this positionbeing in normal nonindicating and nonbypassing position; v

FIG. 7 is a view similar to FIG. 6 but showing the parts in a positionin which the indicator means has been actuated to indicate that acertain predetermined pressure differential limit has been reached;

FIG. 8 is a longitudinal sectional view showing the parts in bypassingposition; and

FIG. 9 is a sectional view taken on the line 9-9 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. I, the numeral11 represents a conduit in the high-pressure side of a fluid system andthe numeral 12 represents a conduit in the low-pressure side. Numeral 14represents a filter device through which fluid is passed in order that afiltering action may be performed on it. In the course of the operationof the system the filter becomes spent and will gradually build up aback pressure so that the differential between the high pressure sideand the low-pressure side will be increased.

My invention is not limited to a system in which a filter is anindispensible unit, the filter being representative of any type of,fluid component in which a pressure drop may exist or be "lief deviceof my invention is indicated by the numeral 15 and is connected to thehigh-pressure side of the system' by'suitable piping or conduit 16 andto the lower side by suitable piping or conduit 17. Thus, it will beseen that the device is in parallel with the filter 14.

Referring now to FIGS. 2 to 5, the details of construction and operationof this form if my invention will be described.

The body is supported in a suitable housing 21, which is connected tothe conduit 16 at 22 and to the conduit 17 for 23. Suitable seals 24 and25 are provided to form a leakage proofspace 16 in the housing 21.

The body 20 has a dividing wall 27 which divides the body into apressure responsive means chamber or piston chamber 28 and an indicatorelement chamber 29. The cylindrical wall 30 forming the chamber orcylinder 28 has an upper bleed 31, a lower bleed 32, and a centralbypass passage or passages 33, the bleed 32 and the bypass passages 33being pressure drop ports whereby the pressure within the lower part ofthe chamber 28 during certain operation may be held above thelow-pressure side of the system.

Within the chamber or cylinder is a differential pressureresponsivemeans or differential pressure piston or sensor piston 35 which has acylindrical portion 36 which has sliding engagement with the cylindricalwall of the piston chamber. The piston 35 is biased in a downwarddirection or toward seat 37 by means ofa compression spring 38, one endof which engages the wall 27 and the other end of which engages theshoulder at the upper end of the cylindrical portion 36. Piston 35 has adiametrical wall 39 from which there extends a cylindrical flange 40,which provides an annular valve edge 41 which, in FIG. 2, is inengagement with the conical valve seat 37.

The valve seat 37 is provided by the upper end ofa seat element 43,which is held in place by rolling or crimping inwardly a flange 44formed at the lower end of the body 20. The seat element has a centralpressure passage 45 which receives fluid under pressure from the conduit16 of FIG. 1. When the piston 35 is in the position shown in FIG. 2 withthe valve edge 41 in engagement with the seat 37, area a of the lowerend of the piston is exposed to high pressure fluid and tends to movethe piston in a direction opposite to the force applied to it by thebiasing spring 38.

Above the diametrical wall 39 is a chamber 47 having a bleed 48, whichchamber slidably supports the indicator-actuating means of my inventionwhich is provided in the form of a magnet 49 stepped at 50 so that thecrimped upper end 51 holds the larger diameter portion of the magnet 49in the chamber 47, the magnet 49 normally being held in extendedposition by a compression spring 53 in the chamber 47. The crimped lip51 acts as a stop, as shown in FIG. 2.

The indicator element of my invention, generally designated by thenumeral 55, has a body 56 supported within the chamber 29, the upper endof the chamber 29 being closed by an iron cap 57 held in place by acrimped lip 54. The recess 58 receives a magnet 59. It will be notedthat the magnets 49 and 59 have like poles on adjacent sides so thatwhen the magnets are brought into adjacency there is a repelling action.The indicator element has a cylindrical indicator portion 60, whichprojects through a central cylindrical opening in the iron end plate 57.There is a compression spring 61 which normally holds the indicatorelement 55 in its retracted position as shown in FIG. 2 with the northpole of the magnet 59 in contact with an iron plate 63 mounted in arecess formed in the dividing wall 27. The pressure of the spring 61plus the magnetic pull of the magnet on the iron plate 63 holds theindicator element 55 in the position shown in FIG. 2. Other than themagnets. the iron cap 57 and the iron disk 63, various parts of myinvention, at least in the adjacency of the magnets, are made ofnonmagnetic material.

As previously pointed out, the parts are shown in FIG. 2 in thepositions which they occupy when there are no unusual pressuredifferential conditions between the high-pressure side and thelow-pressure side of the system. At this time the pressure in thehigh-pressure side presses against the area a of the piston 35 exertinga force in a direction tending to move the piston 35 from the seat 37.At this time, however, there is the pressure of the low pressure side ofthe system plus the force of the biasing spring 38 tending to hold thepiston 35 in seated position. The strength of the biasing spring 38 issuch that its force in combination with the force applied by thelowpressure fluid will hold the piston seated during all normal andusual operations of the system. Should there by any leakage past thevalve 41 the .bleed 32 connected to the space 64 prevents fluid frombuilding up a pressure against the end face 65 of the piston 33, thus,inadvertently or improperly unseating this piston At this time theindicator element 55 is in retracted nonindicating position, being heldin this position by the force of the spring 61 and the magnetic pull ofthe magnet as previously explained.

Whenever an increase in pressure occurs in the high-pressure side of thesystem, or whenever the differential in pressure between thehigh-pressure side and the low-pressure side of the system becomessufficiently large that the force tending to unseat the piston 35 isgreater than the force tending to seat the piston 35, the piston willthen move away from the seat 37. This may occur by a pressure surgeoccurring in the system or may occur by the filter 14 of other elementbuilding up a back pressure such, for example, as would occur if thefilter 14 becomes clogged over a period of use.

When this increase in pressure occurs the parts will ultimately moveinto the position shown in FIG. 3. This action occurs as follows: Thefirst movement of the piston cracks the valve and high pressure now actson the full piston area b "as indicated in FIG. 2. This produces asudden increase in force which, in turn, causes the piston to rapidlytravel in a direction away from the seat 37 until the spring 38 has beensufficiently compressed to again create a condition of equilibriumbetween the spring force and the fluid pressure. This position is shownin FIG. 3. The design of the device is such that this condition willoccurjust before the lower edge 65 of the piston 35 leaves the corner 66of the lower wall or walls of the bypass passage or passages 33. At thistime the main flow through the bypass passages 33 is closed and the onlyflow taking place is that which goes through the bleed port 32 and anyannular clearance between the piston 35 and the bore of the cylinder orchamber 28. This flow rate is predetermined by design requirements forthe device and is a very small volume.

When the piston 35 moves into the position shown in FIG. 3, the northpole of the magnet 49 contacts the bottom face of the wall 27, and therepellent action resulting from like poles being brought adjacent toeach other, produces a repelling force which causes the indicator 55 tomove upwardly to that the body 56 engages the lower face of the ironplate 57, the south pole of the magnet being attracted to the iron body,thus holding the indicator element in this indication position whereinthe cylindrical part 60 projects from the device and indicates thatthere has been an increase in pressure in the high-pressure side of thesystem or that a differential in pressure has reached a predeterminedlimit. Should the piston 35 during this operation over travel theposition shown in FIG. 3, the spring 53 will yield, permitting relativeaxial movement between the piston and the indicator actuator element ormagnet 49.

If the pressure increase in the high-pressure side of the system ismerely a surge in pressure and the pressure after the surge returns tonormal limits, the piston will again return to the position shown inFIG. 2 and operations will continue until a further increase may occur.However, the indicator 55 will remain in its indicating position thustelling an attendant that there has been an exceeding of thepredetermined differential pressure limit and that an investigation ofits cause should be made.

If the differential pressure increases above the pressure differentiallimit required to bring the parts into the position shown in FIG. 3 andcause the actuation of the indicator, the pressure differential or highpressure will be reaching an area beyond which damage might occur. Whenthis first differential pressure is exceeded the piston 35 will thenmove into a position as shown in FIG. 4 to uncover the bypass passagesor ports 33 so that fluid will be bypassed from the high-pressure sideto the lowpressure side flowing through the conduit 16, the device andthe conduit 17. The size of the bypass passages 33 is designed so thatthere will be a pressure drop across them in order to maintain the highpressure necessary to keep the piston in bypassing position during thetime this high pressure continues. When the piston 35 moves from theposition shown in FIG. 3 into the position shown in FIG. 4, there willbe a relative telescoping movement between the magnet 49 and the piston35 whereby the magnets rest almost entirely within the chamber 47.During this movement fluid must be expelled from the chamber 47 and thisfluid will flow through the bleed port 48.

Again, if the high pressure which has caused the parts to move into theposition shown in FIG. 4 is a temporary surge in pressure, the partswill, upon reduction in the pressure surge, return either to theposition shown in FIG. 3 or to the position shown in FIG. 2, except 55remains in extended position until manually reset, depending upon theamount of reduction in pressure.

The form of my invention shown in FIGS. 6 to 9 difiers in certainrespects from the form just described. Generally the inventions are thesame, but the form now under consideration differs from the firstdescribed form in that the indicator actuating means in directly exposedto the pressure on the high-pressure side of the system. Because of thesimilarity of many parts the same numerals will be used. Also because ofsimilarity of functions, it will be unnecessary to describe all thefunctions nor will it be necessary to go into all the functions nor willit be necessary to go into all the details of construction as was donein connection with FIGS. 2 to 5. Where parts perform a similar functionbut are different in form or details of construction, the part numbergiven to that part will be followed by the suffix a. For example theform in FIGS 6 to 9 has a piston which is of different form than theform in FIGS. 2 to 5 and, therefore, this piston will be given theidentification 35a."

Referring to FIG. 6, this view shows the parts in the positions theyoccupy when the system is within normal pressure differential values. Asin the first form, there is a body supported in a housing 21, the body20 having a piston chamber or cylinder 28 which is connected to thelow-pressure side of the system through a bleed passage 31 at its upperpart and through'bypass passages or ports positioned closely adjacent tothe valve seat and, therefore, will be identified as bypass passages orports 33a.

The body 20 is provided with a seat element 43a which is threadedlyconnected to the lower end of the body by a threaded joint I00 and thisseat element carries the lower 0- ring seal 25. The piston 35a isslidable in the chamber 28 and has a tapered valve face 41a whichengages the knife edge seat 370.

In the piston 35a is an opening generally designated by the numeral 101which extends axially from one end to the other end of piston 35a. Theupper portion of this opening is in the form ofa cylinder 102, thecentral portion is in the form of an enlarged chamber 103, and the lowerportion is in the form of a passage 104 which is separated from thechamber I03 by a conical seat 105. Positioned within and supported bythe body 35a is an indicator actuator piston 490 which has a cylindricalbody 107 recessed at its upper end to receive the magnet 108. The body107 is slidable in the bore or cylinder I02 and the lower end of thisbody projects into the chamber 103 and has an O-ring seal I09 supportedin a groove. The relative diameters of the body 107 and the cylinder I02are such as to permit slight leakage However, when the indicatoractuating means 49a is raised into a position as shown in FIG. 2, inwhich the seal 109 is within the bore 102, there is no leakage.

The lower end of the body is of reduced diameter as at 110, and providesa knife edge annular corner III which engages the seat 105. Theindicator actuator is normally held against its seat by a biasing springI12 and when the parts are in the position shown in FIG. 6 the area ofthe piston 49a exposed to the high-pressure side of the system isindicated at a. The area of the piston 35a, exposed to the high-pressureside of the system, is indicated by 0" which is the diameter of theknife edge seat 37a.

Under normal pressure conditions, the parts are as shown in FIG. 6, withboth valve faces against their seats and the indicator 55 in a retractedposition. At this time the pressure differentials are such as to belower than valve cracking" pressure.

Differential pressure against the lower end of the indicator actuatorelement 49a is on the area a" and the high pressure against this area isopposed by the pressure on the low pressure side of the piston plus thespring force I12. If at this time there is a leakage past the seat IIIit is bled through the clearance between the cylinder I02 and thecylindrical body 107. This leakage, of course, is very small and is notconsidered measurable by normal means. The purpose of this bleed between102 and 107 is to prevent pressure buildup which would act on the areab" which would result in actuation at a lower pressure than thepredetermined differential pressure required to move the element 49afrom its seat. The total exposed area of the piston 35a is as indicatedat 0" and the pressure attempting to lift this piston from its seatprior to the actuation of the indicator actuating means 49a is an areaequal to area c" minus area a. The load or force in a direction tendingto move this piston 35a from its seat is balanced by force from thespring 38 plus, of course, the low pressure against the low-pressureside of the piston 35a, this combined force being adequate to hold valve350 closed at all difi'erential pressures below the predeterminedpressure differential at which the indicator is to be actuated.

As the differential pressure reaches the predetermined actuationpressure the pressure acting on area a overcomes the force tending tohold the indicator actuator against its seat and this means 49a willmove away from the seat I05. When this movement occurs the pressure inthe high pressure side of the system then acts on the larger area b" andthe indicator actuator 49a rapidly moves away from the seat until themagnet 108 comes against the wall 27 and into a position as shown inFIG. 7. At this time the indicator 55 moves into an extended oractuating position as explained in connection with the first form of myinvention.

After the parts have moved into the position shown in FIG. 7 the area ofthe piston 35a exposed to the differential position will be an areaequal to c" minus It is to this area that the spring 38 is designed tofunction, and the piston 35a is held against its seat until such time asa higher predetermined differential pressure is reached, at which timethe piston 35a will be moved from its seat. The large area"d" will nowbe exposed to high pressure, and the valve 35a will rapidly move intothe position shown in FIG. 8. Fluid will now bypass through the pressuredrop bypass passages 33a as shown in FIG. 8.

If thereafter the high pressure is reduced, the piston 35a may return toits seat as in FIG. 2 and if the pressure differential reduces furtherand to a normal range, the parts may ultimately return to the positionshown in FIG. 6. As in the first form, however, the indicator 55 remainsin indicating position in order that the attendant may know that therehas been an increase in pressure and that an investigation should bemade to determine its cause and whether or not the filter 14 should bereplaced.

Iclaim:

l. A pressure indicator and bypass pressure relief device for use in asystem having a high-pressure side and a low-pressure side, thecombination including:

a. a movable piston exposed on one side to high pressure and on theother side to low pressure said piston being movable wheneverdifferential pressure exceeds a predetermined minimum;

b. means for indicating a predetermined increase in differentialpressure between the high pressure side and the low-pressure side of thesystem;

0. means for operating said indicator means carried by said piston andexposed directly to high pressure on the highpressure side of saidpiston, said indicator operating means being movable independent of saidpiston to actuate said indicator means upon a predetermined increase indifferential pressure; and

d. means interconnecting said high-pressure side of said piston with thelow-pressure side of the system for relieving pressure on saidhigh-pressure side of said piston when the differential between highpressure and low pressure exceeds a second predetermined limit, saidmeans being in cooperative communication with and operable by saidmovable piston.

2. A pressure indicator and bypass pressure relief device for use in asystem having a high-pressure side and a low-pressure side, thecombination including:

a. a movable piston exposed on one side to high pressure and on theother side to low pressure, said piston being movable wheneverdifferential pressure exceeds a predetermined minimum;

b. means for indicating a predetermined increase in differentialpressure between the high-pressure side and the low-pressure side of thesystem;

c. means for operating said indicator means, said means comprising amovable differential pressure-responsive element carried in said pistonand having a portion exposed directly to the high pressure on thehigh-pressure side of said piston; and

d. means interconnecting said high-pressure side of said piston with thelow-pressure side of the system for relieving pressure on saidhigh-pressure side of said piston when the differential between highpressure and low pressure exceeds a second predetermined limit, saidmeans being in cooperative communication with and operable by saidmovable piston.

3. A pressure indicator and bypass and a pressure relief device, thecombination including:

a. a body having a chamber which has a high-pressure inlet and alow-pressure outlet;

b. pressure responsive means in said chamber exposed to high pressure onone side and low pressure on the other side;

c. means for indicating an increase in differential pressure betweensaid high-pressure side and said low-pressure side;

d. means for operating said indicator means movably carried by saidpressure-responsive means, said indicatoroperating means being movableby an increase in pressure on said high-pressure side of saidpressure-responsive means into a position to actuate said indicatormeans; and

e. means interconnecting the high-pressure side and the low-pressureside of said pressure-responsive means for relieving high pressure onsaid high-pressure side. said means being operable by saidpressure-responsive means as a result of a further increase in pressureon said highpressure side of said pressure-responsive means over andabove that necessary to move said indicator-operating means intoposition to actuate said indicator means.

4. A combination as defined in claim 3 in which a first increase indifferential pressure will cause movement of said pressure-responsivemeans to move said indicator-operating means into a position to actuatesaid indicator means and in which a higher differential pressure willmove said pressure responsive means into bypass pressure relief positionto open a bypass and relieve the pressure on said high-pressure side.

5. A combination as defined in claim 3 in which said indicator meansindicates high-pressure surges on said high-pressure side without theopening of said high-pressure relief means.

6. A pressure indicator and bypass and a pressure relief device, thecombination including:

a. a body having a chamber which has a high-pressure inlet and alow-pressure outlet; b. a cylinder in said chamber exposed to highpressure on one side and low pressure on the other side said cylinderhaving:

1. a seat at the high-pressure side of said cylinder;

2. a bleed means adjacent said seat and in communication with alow-pressure zone in said chamber in said body; and

3. a high-pressure relief port means in said cylinder communicating witha low-pressure zone in said chamber said relief port being spaced afurther distance from said seat then said bleed means;

c. a piston means movable in said cylinder, said piston being adapted tosealably engage said seat in said cylinder and to operate saidhigh-pressure relief port means as the result of an increase indifferential pressure between said high pressure and said low-pressureside of said cylinder;

d. means for indicating an increase in differential pressure betweensaid high-pressure side and said low-pressure side; and

e. means for operating said indicator means carried by said piston, saidindicator operating means being movable by an increase in pressure onsaid high-pressure side of said cylinder into a position to actuate saidindicator means.

1. A pressure indicator and bypass pressure relief device for use in asystem having a high-pressure side and a low-pressure side, thecombination including: a. a movable piston exposed on one side to highpressure and on the other side to low pressure, said piston beingmovable whenever differential pressure exceeds a predetermined minimum;b. means for indicating a predetermined increase in differentialpressure between the high pressure side and the low-pressure side of thesystem; c. means for operating said indicator means carried by saidpiston and exposed directly to high pressure on the highpressure side ofsaid piston, said indicator operating means being movable independent ofsaid piston to actuate said indicator means upon a predeterminedincrease in differential pressure; and d. means interconnecting saidhigh-pressure side of said piston with the low-pressure side of thesystem for relieving pressure on said high-pressure side of said pistonwhen the differential between high pressure and low pressure exceeds asecond predetermined limit, said means being in cooperativecommunication with and operable by said movable piston.
 2. a bleed meansadjacent said seat and in communication with a low-pressure zone in saidchamber in said body; and
 2. A pressure indicator and bypass pressurerelief device for use in a system having a high-pressure side and alow-pressure side, the combination including: a. a movable pistonexposed on one side to high pressure and on the other side to lowpressure, said piston being movable whenever differential pressureexceeds a predetermined minimum; b. means for indicating a predeterminedincrease in differential pressure between the high-pressure side and thelow-pressure side of the system; c. means for operating said indicatormeans, said means comprising a movable differential pressure-responsiveelement carried in said piston and having a portion exposed directly tothe high pressure on the high-pressure side of said piston; and d. meansinterconnecting said high-pressure side of said piston with thelow-pressure side of the system for relieving pressure on saidhigh-pressure side of said piston when the differential between highpressure and low pressure exceeds a second predetermined limit, saidmeans being in cooperative communication with and operable by saidmovable piston.
 3. A pressure indicator and bypass and a pressure reliefdevice, the combination including: a. a body having a chamber which hasa high-pressure inlet and a low-pressure outlet; b. pressure responsivemeans in said chamber exposed to high pressure on one side and lowpressure on the other side; c. means for indicating an increase indifferential pressure between said high-pressure side and saidlow-pressure side; d. means for operating said indicator means movablycarried by said pressure-responsive means, said indicator-operatingmeans being movable by an increase in pressure on said high-pressureside of said pressure-responsive means into a position to actuate saidindicator means; and e. means interconnecting the high-pressure side andthe low-pressure side of said pressure-responsive means for relievinghigh pressure on said high-pressure side, said means being operable bysaid pressure-responsive means as a result of a further increase inpressure on said high-pressure side of said pressure-responsive meansover and above that necessary to move said indicator-operating meansinto position to actuate said indicator means.
 3. a high-pressure reliefport means in said cylinder communicating with a low-pressure zone insaid chamber, said relief port being spaced a further distance from saidseat then said bleed means; c. a piston means movable in said cylinder,said piston being adapted to sealably engage said seat in said cylinderand to operate said high-pressure relief port means as the result of anincrease in differential pressure between said high pressure and saidlow-pressure side of said cylinder; d. means for indicating an increasein differential pressure between said high-pressure side and saidlow-pressure side; and e. means for operating said indicator meanscarried by said piston, said indicator operating means being movable byan increase in pressure on said high-pressure side of said cylinder intoa position to actuate said indicator means.
 4. A combination as definedin claim 3 in which a first increase in differential pressure will causemovement of said pressure-responsive means to move saidindicator-operating means into a position to actuate said indicatormeans and in which a higher differential pressure will move saidpressure responsive means into bypass pressure relief position to open abypass and relieve the pressure on said high-pressure side.
 5. Acombination as defined in claim 3 in which said indicator meansindicates high-pressure surges on said high-pressure side without theopening of said high-pressure relief means.
 6. A pressure indicator andbypass and a pressure relief device, the combination including: a. abody having a chamber which has a high-pressure inlet and a low-pressureoutlet; b. a cylinder in said chamber exposed to high pressure on oneside and low pressure on the other side, said cylinder having: